In recent years, with a sharp increase of transmission service capacity, single-wavelength capacity of an optical backbone DWDM (Dense wavelength division multiplexing, dense wavelength division multiplexing system) network is upgraded from 10 Gb/s to 40 Gb/s. At the same time, a 100 Gb/s single-wavelength rate becomes carriers' next point of interest. Key technologies for achieving this technical upgrade are various advanced modulation technologies, for example, a PDM-BPSK (Polarization Division Multiplexing Binary Phase Shift Keying, polarization division multiplexing binary phase shift keying) modulation technology and a QPSK (Quadrature Phase Shift Keying, quadrature phase shift keying) modulation technology. Different apparatuses may need to be designed for different modulation manners to implement the PDM-BPSK modulation and the QPSK modulation.
A same type of apparatus is capable of implementing only one modulation manner. Therefore, to implement the PDM-BPSK modulation and the QPSK modulation, two different types of apparatus need to be designed, which increases a design cost.